Test device and method for testing mechanical properties of hydrophobic and hydrophilic unsaturated soils

Abstract

A test device and method for testing the mechanical properties of hydrophobic and hydrophilic unsaturated soil, comprising a pressure chamber located at the center of the entire device, an axial loading system located below the pressure chamber, and an axial loading system connected to the pressure chamber through a loading frame; the axial loading system is connected to the information acquisition system; the air pressure control system is located on the side of the pressure chamber and is connected to the pressure chamber through a pipeline; the data acquisition system is located beside the console or computer and is connected to the sensor at each unit; the data processing system is connected to the air pressure control system and the counter pressure control system, and the data processing system is connected to the axial loading system; the sample is located at the center of the pressure chamber; the hydrophobic soil suction control unit and the hydrophilic suction control unit are located at the upper and lower ends of the sample and are in close contact with the sample to ensure uniform pressure transmission, and are connected to the air pressure control system through a pipeline. The present application improves the accuracy and wide applicability of the test of the mechanical properties of unsaturated soil.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering testing equipment technology, specifically to a testing device and method for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soils. Background Technology

[0002] In geotechnical engineering, most soils are unsaturated and can be classified into hydrophilic and hydrophobic soils based on their moisture retention characteristics. Hydrophilic soil particles have strong hydrophilicity, with a contact angle less than 90°. During humidification and dehumidification, the water film is concave, and the pore air pressure is usually greater than the pore water pressure, creating a significant capillary effect. In contrast, hydrophobic soil particles develop a hydrophobic coating due to chemical treatment or natural processes, resulting in a contact angle greater than 90° and significant drainage. In this case, the water film between particles is convex, potentially causing the pore water pressure to be higher than the pore air pressure, a fundamental difference from the characteristics of hydrophilic soils.

[0003] With the continuous advancement of infrastructure construction and environmental engineering practices such as slope engineering, landfill cover engineering, and seepage prevention engineering, hydrophobic soil has gradually become a common type of special soil in these projects. For example, artificial hydrophobic soil is often used to reduce rainwater infiltration, improve slope stability, or as landfill cover material to reduce the risk of groundwater pollution. However, existing unsaturated soil mechanics testing devices are mainly based on axis translation technology, which adjusts suction by controlling the difference between pore air pressure and pore water pressure. However, this technology requires pore air pressure to be greater than pore water pressure, making accurate testing of the suction and mechanical behavior of hydrophobic soil a challenge. This limitation severely restricts the development of unsaturated hydrophobic soil mechanics theory and hinders the optimized design of related projects. Therefore, there is an urgent need for a unified suction control technology and mechanical property testing method applicable to both hydrophilic and hydrophobic soils to meet the needs of engineering practice. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a testing device and method for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soils. This addresses the problem that existing testing devices for unsaturated soil mechanical properties are unsuitable for hydrophobic soils, thus improving the accuracy and applicability of unsaturated soil mechanical property testing. The testing device can be quickly modified from existing unsaturated triaxial equipment, making it highly operable. The testing method fully considers the differences in soil mechanical properties caused by hydrophilicity and hydrophobicity, selecting different suction control units for different soil types, thus providing strong specificity and enabling accurate description of soil mechanical properties.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A test apparatus for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soils includes a pressure chamber located at the center of the apparatus; an axial loading system located below the pressure chamber for applying axial stress, connected to the pressure chamber via a loading frame; a data acquisition system connected to the axial loading system for controlling the loading rate and loading method; a pneumatic control system located on the side of the pressure chamber, connected to the pressure chamber via pipes, acting as a gas pressure pump to provide confining pressure to the pressure chamber and pore pressure to the top of the specimen; a data acquisition system located next to a console or computer, connected to sensors at each unit for measuring and acquiring parameters such as stress, strain, and pore pressure; a data processing system connected to the pneumatic control system and the back pressure control system for real-time monitoring and recording of test data, also connected to the axial loading system for controlling the loading rate and loading method; a specimen located at the center of the pressure chamber; and hydrophobic soil suction control units and hydrophilic suction control units located at the upper and lower ends of the specimen for transmitting pore pressure and back pressure, maintaining close contact with the specimen to ensure uniform pressure transmission, and connected to the pneumatic control system via pipes.

[0007] The hydrophobic soil suction control unit is used to precisely control the pore air pressure at the top of the hydrophobic soil sample.

[0008] The hydrophilic suction control unit is used to precisely control the pore water pressure at the bottom of the hydrophilic soil sample;

[0009] The axial loading system is used to precisely control the magnitude of the axial load on the specimen;

[0010] The air pressure control system is used to precisely control the confining pressure in the pressure chamber and the pore air pressure applied to the top of the sample;

[0011] The back pressure control system is used to apply back pressure to the bottom of the sample;

[0012] The data acquisition system is used to collect data on pore gas pressure, confining pressure, back pressure, and volume deformation during the experiment;

[0013] The data processing system is used to record and process various data during the experiment, and present them in graphical form on the computer.

[0014] The hydrophobic soil suction control unit consists of a layer of expanded polytetrafluoroethylene (e-PTFE) film wrapped around the surface of a porous metal plate structure, and is installed together with the sample cap at the top of the sample. The contact angle of the e-PTFE surface is typically greater than 90°, and can even reach over 120°. This high hydrophobicity prevents water from wetting the film surface, thus preventing liquid water from passing through. Meanwhile, the microporous structure of e-PTFE allows gas molecules to diffuse or flow freely through. The porous metal plate ensures gas passage. Therefore, within a given pressure range, the pore water pressure can exceed the pore gas pressure.

[0015] The pressure chamber includes an outer pressure chamber and an inner pressure chamber. The outer pressure chamber is located between the vertical loading frame and the axial loading control console, while the inner pressure chamber is installed inside the outer pressure chamber.

[0016] The hydrophilic suction control unit is mounted on the base, located at the bottom of the sample, and is made of a high air intake value clay plate;

[0017] The terracotta board is made by mixing kaolin and mineral raw materials such as quartz powder and sintering at high temperature. The board has uniform and continuous micron-sized capillary channels inside, with an average pore size between 0.1 and 1 micron, thus providing an air intake value of 200 to 500 kPa. It can prevent air infiltration under saturation while allowing water to flow freely inside. During the test, the terracotta board is connected to the counterpressure system, which can stably control the pore water pressure inside the soil and establish a constant matrix suction boundary condition when pore air pressure is applied from above. This ensures that the hydrophilic unsaturated soil can achieve reliable suction adjustment and mechanical response testing under axial translation loading mode.

[0018] The high air intake value clay plate is a sintered ceramic material containing a large number of uniformly distributed micropores with a pore size of 0.5 micrometers, which is the same size as the bottom of the sample. The diameter is 40 mm and the thickness is 5 mm-10 mm.

[0019] When the pores inside the high-air-intake clay plate are completely saturated with water, the capillary force formed by the water film on the pore surface will prevent gas from passing through. Therefore, within a given pressure range (0-5 bar), the pore air pressure is greater than the pore water pressure.

[0020] The axial loading system includes a vertical loading frame and an axial loading console. The vertical loading frame is fixed to the crossbeam by screws and the groove at the end of the vertical loading rod is embedded into the protrusion on the sample cap, thereby pressing against and fixing the sample to prevent the force line from shifting.

[0021] The axial loading console has a vertically moving hydraulic rod that applies corresponding axial stress by controlling the vertical displacement; the two work together to complete the axial loading and control of the specimen; the axial loading system is used to apply vertical loads, which are transferred to the upper part of the specimen through the loading head, thereby achieving compression, shear deformation of the specimen.

[0022] The air pressure control system includes an air pressure control box and two gas pipes, namely a confining pressure pipe and a pore air pressure pipe. The confining pressure pipe is connected to the external pressure chamber to provide the corresponding confining pressure, and the pore air pressure pipe is connected to the sample cap to provide the corresponding pore air pressure.

[0023] The outer pressure chamber is used to apply confining pressure, control pore pressure, provide a stable test environment, measure volume changes, and protect the sample. The inner pressure chamber is used to apply confining pressure and control pore pressure to ensure the accuracy and repeatability of test results.

[0024] The external pressure chamber is located between the vertical loading frame and the axial loading control console, while the internal pressure chamber is installed inside the external pressure chamber.

[0025] The outer pressure chamber consists of a metal screw and an organic transparent glass cover, while the inner pressure chamber, also made of high-strength organic transparent glass, is the key component for containing the soil sample and applying confining pressure. It provides a stable pressure environment for the sample, ensuring uniform pressure distribution around the sample during the test, simulating the stress state of soil in actual engineering. A permeable plate at the bottom facilitates the drainage of pore water and the measurement of pore water pressure. The pressure chamber is well-sealed to prevent pressure leakage and ensure the accuracy of the test data. During the test, the confining pressure can be adjusted according to different test requirements to study the effect of confining pressure on the mechanical properties of unsaturated soil.

[0026] like Figure 13 As shown, the back pressure control system includes a pore water pressure sensor, a pressure regulator, and connecting pipelines, used to measure pore water pressure and monitor the pore water pressure inside the soil sample in real time; the pressure regulator is used to adjust the pore water pressure to simulate different unsaturated states.

[0027] The porous metal plate is made of a highly permeable material to ensure efficient gas exchange. The gas valve is adjusted via an external control device to adapt to different test conditions and requirements. The porous metal plate structure is connected to the pressure chamber cap of the triaxial apparatus, and the sample is compressed and sheared by the lifting and lowering of the base. The porous metal plate structure is also connected to a pressure controller to measure and control the pore pressure within the sample.

[0028] The data acquisition system includes a static 8-channel data acquisition instrument and sensor data cables. It is used to acquire experimental data and convert sensor signals into digital signals; the data cables connect to the sensors for real-time recording of experimental data, such as stress, strain, volumetric deformation, pore water pressure, and pore gas pressure.

[0029] The data processing system includes a PLC control system, which is used to process experimental data, display the data in real time in the form of images, and calculate various experimental data, such as stress, strain, volumetric deformation, etc.

[0030] A method for using a test apparatus that can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils includes the following steps: First, the hydrophobicity or hydrophilicity of the soil is determined by a drip test. For hydrophilic soils, a sample is prepared according to the geotechnical testing specifications, with a sample size of 39.1 mm in diameter and 80 mm in height. After saturating the sample, it is installed on the sample base, and the upper and lower ends of the sample are fixed with rubber bands. Then, an outer pressure chamber and an inner pressure chamber are installed, and a water pump is connected to inject de-aired water into the pressure chamber. The suction of the hydrophilic sample matrix is ​​controlled by a hydrophilic suction control unit. The hydrophilic suction control unit only allows water to pass through and does not allow gas to pass through, that is, it ensures that the pore air pressure is greater than the pore water pressure.

[0031] For hydrophobic soils, specimens are prepared according to the same geotechnical testing specifications, with the same specimen dimensions: 39.1 mm in diameter and 80 mm in height. The testing process for hydrophobic soils is similar to that for hydrophilic soils, except that the hydrophilic suction control unit needs to be disassembled, and a hydrophobic suction control unit needs to be installed on top of the specimen. The hydrophobic soil suction control unit ensures that only air can pass through the upper part of the specimen, while water is not allowed to pass through, thus achieving a pore water pressure greater than the pore air pressure, thereby controlling the suction of the hydrophobic soil.

[0032] The beneficial effects of this invention are:

[0033] Traditional experimental methods often fail to consider the hydrophilicity and hydrophobicity of soil. In unsaturated soil experiments, they often assume that pore air pressure is greater than pore water pressure. This can lead to water flowing back into the sample cap when testing hydrophilic unsaturated soil samples, affecting the volume change results. In hydrophobic unsaturated soil tests, the results can deviate significantly from the true values. Therefore, this device effectively improves the accuracy of experimental results for both hydrophilic and hydrophobic soil samples in unsaturated soil experiments, including volume change, pore air pressure, and pore water pressure, making the results closer to the true values. Attached Figure Description

[0034] Figure 1 For unsaturated triaxial compressors and related systems.

[0035] Figure 2 This is a detailed drawing of the loading frame of the present invention.

[0036] Figure 3 Detailed drawing of the external pressure chamber.

[0037] Figure 4 Detailed drawing of the internal pressure chamber.

[0038] Figure 5 Detailed drawings of the sample and base.

[0039] Figure 6 Detailed view of the axial pressure control console.

[0040] Figure 7 An experimental setup for testing the mechanical properties of unsaturated hydrophilic soil and hydrophilic soil.

[0041] Figure 8 An experimental setup for testing the mechanical properties of unsaturated hydrophobic soil and hydrophobic soil.

[0042] Figure 9 This is a detailed drawing of the device.

[0043] Figure 10 Detailed diagram of the suction control unit for hydrophobic soil.

[0044] Figure 11 Detailed diagram of the hydrophilic soil suction control unit.

[0045] Figure 12 This is a schematic diagram of the pressure control box and gas pipeline.

[0046] Figure 13 This is a schematic diagram of the pressure sensor connection.

[0047] Figure label:

[0048] 1: Data processing system; 2: Axial pressure control system; 3: External pressure chamber; 4: Internal pressure chamber; 5: Hydrophobic soil suction control unit; 6: Hydrophilic soil suction control unit; 7: Air pressure control system; 8: Back pressure control system; 9: Data acquisition system; 10: Screw; 11: Crossbeam; 12: Vertical loading rod; 13: Vertical loading rod end groove; 14: Hydraulic rod; 15: Air pressure control box; 16: Gas pipeline; 18: Sample top cap; 20: Metal screw; 21: Organic transparent glass cover; 22: High air intake value terracotta plate. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to the accompanying drawings.

[0050] like Figures 1-13As shown, the purpose of this invention is to provide a test device and method that can uniformly test the mechanical properties of unsaturated hydrophobic soil and hydrophilic soil, so as to solve the problem that the existing test devices for testing the mechanical properties of unsaturated soil cannot be applied to hydrophobic soil, and improve the accuracy and wide applicability of testing the mechanical properties of unsaturated soil.

[0051] A test apparatus for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soils includes a pressure chamber located at the center of the apparatus. An axial loading system 2 is located below the pressure chamber and is used to apply axial stress. The axial loading system 2 is connected to the pressure chamber via a loading frame. The axial loading system 2 is connected to an information acquisition system 1 to control the loading rate and loading method. A pneumatic pressure control system 7 is located on the side of the pressure chamber and is connected to the pressure chamber via a pipe. It acts as a gas pressure pump to provide confining pressure to the pressure chamber and pore air pressure to the top of the specimen. A data acquisition system 9 is located next to a console or computer and is used to measure and acquire parameters such as stress, strain, and pore pressure by connecting sensors at each unit. A data processing system 1 is connected to the pneumatic pressure control system 7 and the back pressure control system 8 to monitor and record test data in real time. The data processing system 1 is also connected to the axial loading system 2 to control the loading rate and loading method. The specimen is located at the center of the pressure chamber. A hydrophobic soil suction control unit 5 and a hydrophilic suction control unit 6 are located at the upper and lower ends of the specimen to transmit pore air pressure and back pressure. They are in close contact with the specimen to ensure uniform pressure transmission and are connected to the pneumatic pressure control system 7 via pipes.

[0052] The hydrophobic soil suction control unit 5 is used to precisely control the pore air pressure at the top of the hydrophobic soil sample.

[0053] The hydrophilic suction control unit 6 is used to precisely control the pore water pressure at the bottom of the hydrophilic soil sample.

[0054] Axial loading system 2 is used to precisely control the magnitude of the axial load on the specimen;

[0055] The air pressure control system 7 is used to precisely control the confining pressure in the pressure chamber and the pore air pressure applied to the top of the sample;

[0056] The back pressure control system 8 is used to apply back pressure to the bottom of the sample;

[0057] The data acquisition system 9 is used to collect data on pore gas pressure, confining pressure, back pressure, and volume deformation during the experiment;

[0058] The data processing system 1 is used to record and process various data during the experiment and present them in graphical form on the computer.

[0059] This device mainly includes the following parts:

[0060] 1. Special Thin Film Material: A high-molecular-weight expanded polytetrafluoroethylene (e-PTFE) film with specific microstructure and physicochemical properties is selected. This film's pore size allows gas molecules to pass freely but significantly impedes water molecules, making it a high-molecular-weight waterproof filter membrane material. It features high porosity and uniform micropore distribution, thus achieving the function of allowing only air to pass through while preventing water from entering. Its micropore size is between 10 nanometers and 100 nanometers, which is very small relative to water droplets, making it impossible for water to pass through, but relatively large for air molecules, allowing air to pass through smoothly. The film also exhibits good aerophilic and hydrophobic properties, further enhancing its selective permeability to gases and water.

[0061] 2. Membrane Fixing Structure: A specialized fixing structure is designed to securely and smoothly fix the membrane to the upper part of the unsaturated soil sample. The fixing structure is made of a high-strength, corrosion-resistant material, namely a porous thin stainless steel plate. The shape and size of the structure are adapted to the sample of the triaxial compression apparatus, with a diameter of 50 mm and a thickness of 5 mm, to ensure that it will not affect the stress and deformation of the sample during the test.

[0062] The relationship between special thin film materials, thin film fixing structures, and unsaturated triaxial compressors and related systems is specifically constituted by a layer of expanded polytetrafluoroethylene (e-PTFE) film wrapped around the surface of a porous metal plate structure. Figure 10 ), often with sample caps ( Figure 9 Installed together and located on top of the sample, it ensures that the back pressure on the sample is greater than the pore air pressure when testing hydrophobic soil, thus precisely controlling the suction force.

[0063] Test method:

[0064] Determine whether the soil is hydrophilic or hydrophobic:

[0065] Water Drop Test: This test measures the contact angle of soil using an optical contact angle meter. The procedure involves pressing a soil sample into a 1cm thick sheet or a flat surface, and then placing a drop of water on the soil surface. The shape of the water droplet is recorded, and the contact angle is determined using the Young's-Laplace equation. A contact angle less than 90° indicates hydrophilic soil, while a contact angle greater than 90° indicates hydrophobic soil.

[0066] Sample preparation:

[0067] For remolded soil samples, calculate the required dry soil mass and water volume based on the predetermined dry density and moisture content. Crush and sieve the air-dried soil sample, typically using a 2mm sieve to ensure particle uniformity. Weigh a certain mass of dry soil according to the calculated amount and place it in a mixing container. Slowly add the corresponding amount of water while thoroughly mixing to ensure the water is evenly distributed among the soil particles, forming the remolded soil sample. Seal the mixed remolded soil sample and let it stand for a period of time, generally 24 hours, to allow for further even distribution of moisture and to allow for some interaction and adjustment between the soil particles.

[0068] Sample installation:

[0069] (1) Select a suitable rubber membrane: Select a rubber membrane of appropriate thickness and size according to the size of the sample. The rubber membrane should have good elasticity and sealing properties, and be free from damage and leaks. Before use, carefully check the integrity of the rubber membrane, and replace it in time if there are any defects.

[0070] (2) Cover with a rubber membrane:

[0071] Place the rubber membrane over the membrane holder, folding both ends outwards and securing it with rubber bands. Inject a suitable amount of water or air into the membrane holder to slightly inflate the rubber membrane, making it easier to fill with the soil sample later. Carefully place the prepared remolded soil sample into the rubber membrane inside the membrane holder, minimizing gaps or wrinkles between the soil sample and the membrane. Special tools can be used to assist in placing the soil sample, ensuring it is centered and neatly shaped within the membrane. Remove the rubber membrane containing the soil sample from the membrane holder and secure both ends of the membrane to the top and bottom of the soil sample with rubber bands to ensure a good seal.

[0072] (3) Install the sample in the pressure chamber:

[0073] Place the sample with the rubber diaphragm installed onto the base of the triaxial pressure chamber. Adjust the sample position and place a layer of filter paper at the bottom and top of the sample. For hydrophilic soils, place a permeable stone with a high air permeability on top of the sample; for hydrophobic soils, place this device (a layer of expanded polytetrafluoroethylene (e-PTFE) film and a porous metal plate structure) on top of the sample. Install the top cover of the pressure chamber, ensuring a good seal between the top cover and the base to prevent pressure leakage. During installation, take care to avoid collisions or disturbances to the sample.

[0074] Instrument debugging and parameter setting:

[0075] (1) Inspect the triaxial compressor:

[0076] Check that all components of the triaxial compressor are functioning properly, including the pressure control system, displacement measurement system, pore water pressure measurement system, and pore gas pressure measurement system. Ensure that all piping connections are tight and free of looseness or leaks. Calibrate the instrument's sensors to ensure the accuracy of the measurement data.

[0077] (2) Set the test parameters:

[0078] According to the test requirements, set the initial values ​​of confining pressure, pore water pressure, pore air pressure, and loading rate. The initial values ​​of pore water pressure and pore air pressure should be reasonably set based on the soil sample saturation and the expected test conditions. The loading rate should be moderate, ensuring accurate capture of the soil sample's mechanical response without making the test process too slow or too rapid.

[0079] Experimental procedure:

[0080] (1) Apply confining pressure:

[0081] Activate the pressure control system and slowly apply the confining pressure to the predetermined value at a rate of 10 kPa / min to 25 kPa / min. During the application of the confining pressure, closely observe the pressure changes and the deformation of the sample to ensure that the confining pressure is applied stably and uniformly.

[0082] (2) Apply pore water pressure and pore gas pressure:

[0083] Apply a predetermined air pressure to the sample. The predetermined air pressure should be equal to the applied matrix suction force. It should be applied uniformly to the predetermined value at a rate of 10 kPa / min to 25 kPa / min. At the same time, the pressure in the inner and outer pressure chambers should be increased by the same value so that the pressure in the inner and outer chambers is always 5 kPa higher than the air pressure.

[0084] For hydrophilic soils, the applied pore air pressure is generally required to be greater than the pore water pressure, and the pore water pressure must be greater than 0.

[0085] If the soil is hydrophobic, the applied pore water pressure is greater than the pore air pressure.

[0086] (3) Axial loading:

[0087] Once the pore water pressure, pore air pressure, and confining pressure have stabilized at their set values, the axial loading system is activated, and the specimen is axially loaded at a predetermined loading rate. During loading, data such as axial load, axial displacement, pore water pressure, and pore air pressure are recorded in real time. Loading continues until the specimen fails or reaches the predetermined axial strain value. During loading, the failure mode and process of the specimen are carefully observed, such as whether obvious cracks, bulging, or shear failure occur.

[0088] Experiment End and Data Processing:

[0089] (1) End of experiment:

[0090] When the soil sample reaches the predetermined value, stop loading. Record all data at the end of the experiment, including the failure stress and failure strain of the soil sample.

[0091] (2) Data processing:

[0092] The experimental data were processed and analyzed to plot stress-strain curves, pore water pressure-strain curves, etc. Based on the experimental results, the strength, deformation characteristics, and failure mechanisms of hydrophilic or hydrophobic soils were evaluated.

Claims

1. A method for using a test apparatus capable of uniformly testing the mechanical properties of unsaturated hydrophobic and hydrophilic soils, characterized in that, The apparatus includes a pressure chamber located at the center of the entire apparatus. An axial loading system (2) is located below the pressure chamber and is used to apply axial stress. The axial loading system (2) is connected to the pressure chamber via a loading frame. The axial loading system (2) is connected to an information acquisition system (1) to control the loading rate and loading method. A pneumatic control system (7) is located on the side of the pressure chamber and is connected to the pressure chamber via a pipe. It acts as a gas pressure pump to provide confining pressure to the pressure chamber and pore pressure to the top of the sample. A data acquisition system (9) is located next to a console or computer and is connected to sensors at each unit. The data processing system (1) is used to measure and collect parameters of stress, strain, and pore pressure. The data processing system (1) is connected to the air pressure control system (7) and the back pressure control system (8) to monitor and record test data in real time. The data processing system (1) is connected to the axial loading system (2) to control the loading rate and loading method. The sample is located at the center of the pressure chamber. The hydrophobic soil suction control unit (5) and the hydrophilic suction control unit (6) are located at the upper and lower ends of the sample to transmit pore air pressure and back pressure. They are in close contact with the sample to ensure uniform pressure transmission and are connected to the air pressure control system (7) through a pipe. The method of using the device includes the following steps: First, the hydrophilicity or hydrophobicity of the soil is determined by a drip test. For hydrophilic soil, a sample is prepared according to the geotechnical test specification. The sample size is 39.1 mm in diameter and 80 mm in height. After saturating the sample, it is installed on the sample base and the upper and lower ends of the sample are fixed with rubber bands. Then, the outer pressure chamber (3) and the inner pressure chamber (4) are installed. A water pump is connected to inject airless water into the pressure chamber. The hydrophilic suction control unit (6) controls the suction of the hydrophilic sample matrix. The hydrophilic suction control unit (6) only allows water to pass through and does not allow gas to pass through, that is, it ensures that the pore air pressure is greater than the pore water pressure. For hydrophobic soil, a sample is also prepared according to the geotechnical test specification. The sample size is also 39.1 mm in diameter and 80 mm in height. mm; The test process for hydrophobic soil differs from that for hydrophilic soil in that the hydrophilic suction control unit (6) needs to be disassembled and a hydrophobic suction control unit (5) is installed on the top of the sample; The hydrophobic soil suction control unit (5) ensures that only air enters the upper part of the sample and water is not allowed to pass through, that is, the pore water pressure is greater than the pore air pressure, thereby achieving control of the suction of hydrophobic soil.

2. The method of using the test apparatus for uniformly testing the mechanical properties of unsaturated hydrophobic and hydrophilic soils according to claim 1, characterized in that, The hydrophobic soil suction control unit (5) is used to precisely control the pore air pressure at the top of the hydrophobic soil sample. The hydrophilic suction control unit (6) is used to precisely control the pore water pressure at the bottom of the hydrophilic soil sample; The axial loading system (2) is used to precisely control the magnitude of the axial load on the specimen; The air pressure control system (7) is used to precisely control the confining pressure in the pressure chamber and the pore air pressure loaded on the top of the sample; The back pressure control system (8) is used to apply back pressure to the bottom of the sample; The data acquisition system (9) is used to collect data on pore gas pressure, confining pressure, back pressure, and volume change during the experiment; The data processing system (1) is used to record and process various data during the experiment and present them in the computer in graphical form.

3. The method of using the test apparatus according to claim 1, which can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils, is characterized in that... The hydrophobic soil suction control unit (5) consists of a layer of expanded polytetrafluoroethylene film wrapped around the surface of a porous metal plate structure, and is installed together with the sample cap, located on the top of the sample.

4. The method of using the test apparatus according to claim 1, which can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils, is characterized in that... The hydrophilic suction control unit (6) is usually installed on the base and located at the bottom of the sample. It is made of a high air intake value clay plate (22). The clay plate is made by mixing kaolin and mineral raw materials such as quartz powder and sintering at high temperature. The plate has uniform and continuous micron-level capillary channels inside, with an average pore size between 0.1 and 1 micron. It has an air intake value of 200 to 500 kPa. During the test, the clay plate is connected to the counterpressure system to stably control the pore water pressure inside the soil. When the pore air pressure is applied above, a constant matrix suction boundary condition is established to ensure that the hydrophilic unsaturated soil can achieve reliable suction adjustment and mechanical response testing under the axial translation loading mode. The high air intake value clay plate (22) is a sintered ceramic material containing a large number of uniformly distributed micropores with a pore size of 0.5 micrometers, which is consistent with the size of the bottom of the sample, with a diameter of 40 mm and a thickness of 5 mm-10 mm. When the pores inside the high air intake clay plate (22) are completely saturated with water, the capillary force formed by the water film on the pore surface will prevent the gas from passing through. Therefore, within a given pressure range, the pore air pressure is greater than the pore water pressure.

5. The method of using the test apparatus according to claim 1, which can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils, is characterized in that... The axial loading system (2) includes a vertical loading frame and an axial loading console. The vertical loading frame is fixed by tightening the crossbeam (11) with two pairs of screws (10) and embedding the groove (13) at the end of the vertical loading rod (12) into the protrusion on the sample cap, thereby supporting and fixing the sample and preventing the force line from shifting. The axial loading console has a vertically movable hydraulic rod (14) that applies the corresponding axial stress by controlling the vertical displacement.

6. The method of using the test apparatus according to claim 1, which can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils, is characterized in that... The air pressure control system (7) includes an air pressure control box (15) and two gas pipes (16). The gas pipes 16 are a confining pressure pipe and a pore air pressure pipe, respectively. The confining pressure pipe is connected to the external pressure chamber (3) to provide the corresponding confining pressure, and the pore air pressure pipe is connected to the sample top cap (18) to provide the corresponding pore air pressure. The outer pressure chamber (3) is used to apply confining pressure, control pore pressure, provide a stable test environment, measure volume changes, and protect the sample. The inner pressure chamber (4) is used to apply confining pressure and control pore pressure to ensure the accuracy and repeatability of the test results. The external pressure chamber (3) is located between the vertical loading frame and the axial loading control console, and the internal pressure chamber (4) is installed inside the external pressure chamber.

7. The method of using the test apparatus according to claim 6, which can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils, is characterized in that... The external pressure chamber (3) is composed of a metal screw (20) and an organic transparent glass cover (21). The internal pressure chamber (4) provides a stable pressure environment for the sample, ensuring that the pressure around the sample is evenly distributed during the test, simulating the stress state of the soil in actual engineering. The bottom of the sample is equipped with a high air intake value clay plate (22) to facilitate the discharge of pore water and the measurement of pore water pressure.

8. The method of using the test apparatus according to claim 1, which can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils, is characterized in that... The back pressure control system (8) includes a pore water pressure sensor, a pressure regulator and connecting pipelines, used to measure pore water pressure and monitor the pore water pressure inside the soil sample in real time; the pressure regulator is used to adjust the pore water pressure to simulate different unsaturated states. The porous metal plate of the hydrophobic soil suction control unit (5) is made of a highly permeable material to ensure gas exchange efficiency; the air valve is adjusted by an external control device to adapt to different test conditions and requirements. The porous metal plate structure is connected to the pressure chamber of the triaxial apparatus, and the sample is compressed and sheared by the lifting and lowering of the base. The porous metal plate structure is connected to a pressure controller to measure and control the pore pressure in the sample.

9. The method of using the test apparatus according to claim 1, which can uniformly test the mechanical properties of unsaturated hydrophobic and hydrophilic soils, is characterized in that... The data acquisition system (9) includes a static 8-channel data acquisition instrument and a sensor data cable, used to acquire experimental data and convert sensor signals into digital signals; the data cable connects to the sensor for real-time recording of experimental data; The data processing system (1) includes a PLC control system for processing experimental data, displaying the data in real time in the form of images, and calculating various experimental data.

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